1. Field of the Invention
The present invention relates to a light-emitting element that has a structure interposing a plurality of layers between a pair of electrodes, in particular, relates to a structure of the layers.
2. Description of the Related Art
A light-emitting device utilizing a light emission from an electroluminescent element (a light-emitting element) has been attracting attention as a device, for example, for displaying or for lighting.
As the light-emitting element that is used for the light-emitting device, an element that has a structure interposing a plurality of layers, each including a material such as a luminescent or carrier transporting material, between a pair of electrodes is well known.
In the case of this light-emitting element, one of the electrodes functions as an anode while the other electrode functions as a cathode, a hole injected from the anode side and an electron injected from the cathode side are recombined to form a molecule in a excited state, and light is emitted when the molecule returns to the ground state. The emitted light is extracted outside through one or both of the pair of electrodes.
As for a manufacturing process of the light-emitting element above, it is commonly known to form one of the electrodes, form the plurality of layers thereon, and form the other electrode further thereon.
In the case of manufacturing the light-emitting element in this way, the layers are sometimes so damaged in the process of forming the electrode after forming the plurality of layers that favorable characteristics cannot be obtained. This phenomenon is frequently observed particularly in the case of using sputtering to form the electrode. This is believed to be because high-energy atoms damage the layers in the process of using sputtering to form the electrode.
Consequently, a light-emitting element comprising a structure that is less subjected to damage even in the case of using sputtering to form the electrode and a manufacturing method thereof have been developed.
For example, Patent Document 1 or Patent Document 2 shows that damage to an organic layer, which is caused during deposition by sputtering, can be suppressed by providing a layer including phthalocyanine. In addition, Patent Document 3 also reports that damage to an organic layer, which is caused during deposition by sputtering, can be suppressed by providing a layer including AgLi.
However, the method shown in Patent Document 1 or Patent Document 2 may have problems that, for example, a process is increased for providing the layer including phthalocyanine between an electron transporting layer and an electron injecting electrode and the luminous efficiency in a red light emission is decreased due to phthalocyanine that absorbs light in a long wavelength range easily. In addition, the method shown in Patent Document 3 may have problems that, for example, as the film thickness of AgLi becomes thicker, the transmissivity of light becomes lower to decrease the external extraction efficiency of emitted light.
[Patent Document 1] Japanese Patent Laid-Open No. 2002-75658
[Patent Document 2] Japanese Patent Laid-Open No. 2002-359086
[Patent Document 3] Japanese Patent Laid-Open No. 2003-249357